[Android Q&A, Help & Troubleshooting] impactor:
This is mount log:

mount
rootfs on / type rootfs (ro,noatime)
tmpfs on /dev type tmpfs (rw,noatime,mode=755)
devpts on /dev/pts type devpts (rw,noatime,mode=600)
proc on /proc type proc (rw,noatime)
sysfs on /sys type sysfs (rw,noatime)
tmpfs on /mnt/asec type tmpfs (rw,noatime,mode=755,gid=1000)
tmpfs on /mnt/obb type tmpfs (rw,noatime,mode=755,gid=1000)
/dev/block/mtdblock3 on /system type yaffs2 (ro,relatime)
/dev/block/mtdblock5 on /data type yaffs2 (rw,nosuid,nodev,relatime)
/dev/block/mtdblock4 on /cache type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mmcblk0p1 on /mnt/sdcard type vfat (rw,noatime,fmask=0022,dmask=0022,codepage=cp437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro)
/dev/block/mmcblk0p2 on /data/sdext2 type ext4 (rw,relatime,commit=15,barrier=1,stripe=64,data=ordered,noauto_da_alloc,discard)
/dev/block/mtdblock5 on /mnt/asec/mtddata type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mmcblk0p2 on /data type ext4 (rw,noatime,commit=15,barrier=1,stripe=64,data=ordered,noauto_da_alloc,discard)
/dev/block/mtdblock5 on /data/local type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/property type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/misc type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/system type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.android.providers.downloads type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.android.providers.downloads.ui type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.android.providers.userdictionary type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.android.providers.calendar type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.android.providers.applications type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.android.providers.media type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.android.providers.drm type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.android.providers.subscribedfeeds type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.android.providers.telocation type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.android.providers.contacts type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.android.providers.settings type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.android.providers.telephony type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.google.android.location type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.android.defcontainer type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.android.contacts type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.android.phone type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/net.cactii.flash2 type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.miui.player type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.android.htmlviewer type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.android.bluetooth type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.android.calendar type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.android.browser type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.miui.backup type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.miui.antispam type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.miui.cloudservice type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.android.certinstaller type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.miui.uac type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.android.thememanager type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.google.android.gms type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.android.settings type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.android.fileexplorer type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.miui.providers.userbook type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.android.wallpaper.livepicker type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.android.packageinstaller type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.svox.pico type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.android.monitor type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.miui.fmradio type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.android.server.vpn type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.android.vending.updater type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.google.android.onetimeinitializer type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.google.android.partnersetup type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.miui.camera type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.android.stk type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.android.sidekick type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/android.tts type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.gau.go.launcherex.gowidget.weatherwidget type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.google.android.syncadapters.calendar type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.avast.android.antitheft type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.google.android.apps.uploader type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.miui.control.panel type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.android.systemui type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.android.deskclock type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.android.spare_parts type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.google.android.gsf type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.google.android.syncadapters.contacts type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/com.google.android.backup type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mmcblk0p2 on /sd-ext type ext4 (rw,nosuid,nodev,noatime,nodiratime,commit=15,barrier=1,stripe=64,data=ordered,noauto_da_alloc,discard)
/dev/block/mtdblock5 on /mnt/sdcard/cache/download type yaffs2 (rw,nosuid,nodev,noatime)
/dev/block/mtdblock5 on /data/data/misc type yaffs2 (rw,nosuid,nodev,noatime)

So apparently the sd card is mountes as RW, but none of the programs can write to it. I even backed it up, reformatted to fat32 and coppied back the data, but it is still the same...

What could that be?